In certain rear wheel drive (RWD) vehicle transmissions, such as in a six-speed RWD automatic transmission of the type known in the art having three gear sets and five torque transmitting elements or clutches, one of the five clutches can be applied in engine braking first gear, manual low, and reverse transmission operating modes. Therefore, such a clutch is referred to functionally as a “low and reverse clutch”, and is selectively engaged or disengaged to enable the operating modes listed above. The input member of the low and reverse clutch can also be selectively connected to a conventional one-way clutch in order to selectively prevent relative rotation of members of two of the gear seats of the transmission when engaged.
In all other forward gears, i.e., in second-through-sixth gear in the conventional six-speed RWD automatic transmission mentioned above, reaction torque does not act on the one-way clutch due to the application or engagement of one or more of the four other clutches in the transmission. Consequently, the one-way clutch rotates freely or “freewheels”, that is, with relative motion being present between the input and output members of the low and reverse clutch. Moreover, the relative speed of such rotation tends to increase with each successive gear change.
As is known in the art, a disengaged multi-plate clutch can produce drag or spin losses whenever relative motion is present between the input and output members of the multi-plate clutch. The spin losses can in turn reduce fuel economy. As the low and reverse clutch is disengaged in most of the forward gears of the RWD transmission described above, except for engine braking first gear and manual low, and as most of the time such a transmission operates in one of these forward gear ratios, a modest but measurable amount of the spin loss occurs when the low and reverse clutch is disengaged.